Using magnetic coupling to improve multiple resonance NMR probe circuits.

Multiple resonant NMR circuits are an especially important aspect of modern NMR detectors. Today NMR researchers can carry out direct observe, indirect observe and double or triple resonance experiments on many different nuclides without having to change the NMR probe. The price for this convenience is loss of efficiency.

RF shielding and eddy currents in NMR probes.

Shielding of the NMR sample by a thin coating of metal between the sample and the rf coil arises in some geometries. The shielding may be used for rf heating of the sample tube or for a high infrared reflectivity coating in cryoprobe applications. An important application is for a shield that prevents noise from entering the rf probe circuit while allowing pulsed magnetic field gradients or field modulation to pass.

Circuit filling factor (CFF) for multiply tuned probes, revisited.

The concept of circuit filling factor (CFF) is re-examined for multi-tuned, multi-inductor probe circuits. The CFF is the fraction of magnetic stored energy residing in the NMR coil. The CFF theorem states that the CFF sums to unity across all the resonant normal modes.

Improving the Mass-Limited Performance of Routine NMR Probes using Coupled Coils.

We report a method to convert, on demand, a general use dual-broadband probe to a high performance mass-limited probe for both high band and low band nuclei. This technology uses magnetic coupling of inductors to achieve this capability. The method offers a cost effective way of increasing the performance of routine NMR probes without having to change probes or increase the overall foot print of the spectrometer.

Using magnetic coupling to implement (1)H, (19)F, (13)C experiments in routine high resolution NMR probes.

We report in this paper the design of (1)H, (19)F, (13)C circuitry using magnetic coupling which can do on demand experiments where one of the three nuclei is observed and the other two are decoupled. The implementation of this circuitry in routine NMR probes is compared with capacitive coupling methods where it was found that by using magnetic coupling the performance of the routine NMR probe was not impacted by the addition of this circuitry. It is surmised that using this type of circuitry would be highly desirable for those chemists doing routine (19)F NMR.

Using Magnetic Coupling to Improve the (1)H/(2)H Double Tuned Circuit.

We report in this paper an analysis of double-tuned (1)H/(2)H circuits that are capacitively or inductively matched to 50 Ω ports. In this analysis we use a novel new parameter called the circuit fill factor (CFF). It provides a means of characterizing the performance degradation associated with additional inductors in the circuit in addition to circuit losses.

Measuring material susceptibility using NMR.

We report on a method of measuring the high-field susceptibilities of paramagnetic and diamagnetic materials using only a standard NMR system equipped with pulsed field gradients. We demonstrate the accuracy and sensitivity of the technique by measuring a series of 99.9% copper wires with diameters between 0.